Don't expand name of ctor default arg

Author: som-snytt

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -477,7 +477,10 @@ object SymDenotations {
 
     /** The expanded name of this denotation. */
     final def expandedName(using Context): Name =
-      if (name.is(ExpandedName) || isConstructor) name
+      if name.is(ExpandedName) || isConstructor
+      || name.is(DefaultGetterName) && name.match { case DefaultGetterName(nme.CONSTRUCTOR, _) => true case _ => false }
+      then
+        name
       else name.expandedName(initial.owner)
         // need to use initial owner to disambiguate, as multiple private symbols with the same name
         // might have been moved from different origins into the same class

compiler/src/dotty/tools/dotc/transform/ExpandPrivate.scala

@@ -25,8 +25,8 @@ import ValueClasses.*
  *  This is necessary since private methods are not allowed to have the same name
  *  as inherited public ones.
  *
- * Also, make non-private any private constructor that is annotated with `@publicInBinary`.
- * (See SIP-52)
+ *  Also, make non-private any private constructor that is annotated with `@publicInBinary`.
+ *  (See SIP-52)
  *
  *  See discussion in https://github.com/scala/scala3/pull/784
  *  and https://github.com/scala/scala3/issues/783

tests/pos/i23477.scala

@@ -0,0 +1,4 @@
+//> using options -Ycheck:expandPrivate
+
+class C private (x: Int, y: Int = 1):
+  def this() = this(1)